Rebels in Aleppo continue to prepare for the defence of the cityAhmad Gharabli/AFP/Getty Images

The international community made a last-ditch diplomatic effort on the crisis in Syria as violence escalated across the country. But even as the UN General Assembly passed a resolution denouncing the use of heavy arms against the opposition, rebels in Aleppo chanted “Assad must die!” and prepared for even more intense fighting.

For many in the urban battlefields of Syria, the resignation of Kofi Annan, the UN peace envoy, marks a new phase in which force rather than diplomacy will be the decisive factor in the future of the Assad regime.

A senior UN peacekeeper, Hervé Ladsous, warned in a briefing to the UN Security Council that Aleppo, Syria’s most populous city, faced a military showdown bigger than anything so far. “The spiral of violence…